System for remotely controlling a radio receiver



Feb. 118, 1936. BLATTERMAN 2,931,555

SYSTEM FOR REMOTELY CONTROLLING A RADIO RECEIVER Filed April 30, 1931 5Sheets-Sheet l uilberi fiBlafierman/ Feb. 18, 1936. A. s. BLATTER'MAN2,031,555 7 SYSTEM FOR REMOTELY CONTROLLING A RADIO RECEIVER.

Filed April 30, 1951. 5 Sheets-Sheet 3 540 KC. ENVELOPE AUDIO FRE UENYFeb. 18, 1936. 5. BLATTERMAN 2,031,555

SYSTEM FOR REMOTELY CONTROLLING A RADIO RECEIVER Filed April 30, 1931 5Sheets-Sheet 4 2-K AMPLIFIER 0F RECEIVER RECEIVE/2- Feb. 18, 1936. I A;s. BLATTERMAN 2,031,555

SY STEM FOR REMOTELY CONTROLLING A RADIO RECEIVER Filed April 50, 1931 5Sheets-Sheet 5 TO TRANSFORMER SUPPLY/N6 POWER TO RECEIVE z gmmloz RFAUNITED STATES PAT'E'T OFFICE SYSTEM FOR REMOTELY CONTROLLING A RADIORECEIVER Albert S. Blatterman, Asbury Park, N. J. Application April 30,1931, Serial No. 534,080

6 Claims.

This invention relates to a system for effecting the entire remotecontrol of a radio receiver or other apparatus from a remote point overthe power or lighting lines which supply the receiver or apparatusitself with operating power.

In general, the present invention is a carrying forward of the remotecontrol system of the type described in my Patent No. 1,856,310, March3, 1932, in which the entire operation of the radio receiver includingits tuning, its volume of response regulation, and the turning of thereceiver on or off is accomplished by means of a readily portablecontrol unit which is connected to the usual house lighting lines andwhich, broadly speaking, comprises a generator of high frequencyoscillations which are constrained to flow over the light lines to thepoint where the receiver is located, the control of the receiver beingaccomplished by these oscillations as described in the patent aforesaid.In that connection, however, it is pointed out that the presentinvention has general application to any system of remote controloperation in which the control is accomplished by the use of high frequency currents transmitted from a control point over electricalconductors to the point where the apparatus is to be contained orlocated. Since high frequency oscillatory currents exist in sys'-' tems.of the class herein referred to, and since in general such systems areresponsive over a rela-' tively wide band of frequencies, it is to beexpected that certain interference effects may nor-' ma-lly beexperienced not only on the receiving system which is itself beingremotely controlled, but on other receiving sets in the neighborhood.

Accordingly, a primary object of the invention is to carry forward theessential principles and features of the patent hereinbefore referred toand to provide methods and means for preventing various kinds ofinterference that may be encountered in the practical use of such remotecontrol systems.

Other objects of the invention will more readily appear as the nature ofthe invention is better understood, the same consisting in the novelconstruction, combination and arrangement of parts hereinafter morefully described, illustrated and claimed.

' Certain preferred and practical embodiments of the invention are shownin the accompanying drawings in which:-

Figure 1 is a diagrammatic view illustrating certain of the elements of'a remote control system of the class here under consideration.-

Figure 2 is a diagram illustrating a modifica-- tion of the circuitarrangements whereby interference in neighboring circuits is prevented.

Figure 2a is a diagram illustrating a further modification by whichinterference in neighboring circuits is prevented.

Figure 22) illustrates, diagrammatically, a third modification whichprevents neighboring circuits.

Figure 3 is a diagram illustrating, schematically, remote controlsystems located in adjacent apartments.

Figure 4 is a diagram illustrating two adjacent interconnected remotecontrol systems, together with means which I have invented to preventinterference between the two systems.

Figure 5 is a detailed diagrammatic view illustrating one of theinterference preventing elements used in Figure 4.

Figure 5a illustrates a modification of the interference preventingelement shown in Figure 5.

Figure 6 is a diagram explaining the elimination of conjugate signalbeat interference.

Figure '7 is a diagram explaining the suppres sion of cross-molulationinterference.

Figure 8 is a diagram illustrating a circuit arrangement by means ofwhich short wave interference is prevented.

Figure 9 is a diagram illustrating a further modification of theinvention by which short wave interference is prevented.

Figure 10 is a diagram showing a circuit used for the regulation ofreceiver sensitivity by remote control.

Figure 11 is a. diagram illustrating a further modifiedv form of circuitfor the regulation of receiver sensitivity-by remote control.

Figure 12 is a diagram illustrating a practical embodiment of theinvention in a complete remote control system. 1

Referring to the type of remote control system set forth in Patent No.1,856,310, certain of the interference dimculties that may beexperienced in the practical use of such systems, together with remedialmeasures to reduce or eliminate such interference when it isencountered, will be briefly explained. For convenience the severaltypes of interference may be classified under the following generalheadings, via: (1) Antenna radiation; (2) Cross-talk between circuits;(3) Conjugate signal beats; (4) Cross-modulation; (5) Image signals; (6)Harmonic interference; (7) Static and background interference.

Antenna radiation.In the class of remote control systems here underconsideration, it will be observedfromFig'ure 1, that high frequencycurinterference in ent.

rent is transmitted from the remote control device C over the houselighting lines L L to a pick-up coil system 3-4 and thence to ground atG. G indicates the electric companies ground on the lines. The highfrequency current referred to passing through coil 3, induces a highfrequency voltage in the associated coil 4 which, as seen in Figure 1,is connected to the antenna A and also to the ground G. As a result,therefore, the high frequency voltage in the coil 4, produced asdescribed by the high frequency remote control line current, produces asimilar high frequency current in the antenna-ground system and thelatter as a consequence acts like a low power transmitting stationradiating high frequency energy which may cause interference in neighborreceivers.

In order to overcome this class of interference it is proposed to carryforward the principles of the aforesaid copending patent, and for thetypical and common case of broadcast reception for example, to selectthe remote control frequency or frequencies transmitted over the lightlines to be either above or else below the band of frequencies used forbroadcasting and, at the same time making such other concomitantapparatus arrangements as may be required by such frequency selection inaccordance with the principles and features prescribed for such controlcurrent frequencies in my aforementioned copending pat- Under theseconditions it will be clear that any antenna radiations of the kindreferred to will cause no neighborhood interference within thebroadcasting spectrum because such radia tion will then occur atfrequencies beyond the frequency range of neighboring broadcastreceivers.

Another remedy proposed to overcome this class of interference isillustrated in Figure 2 wherein an additional vacuum tube 5 is employedin the mixing box with its grid connected to input coil 1 and antenna A.Signals from the antenna are repeated into the plate circuit of the tube5 where they are in this case mixed with the high frequency controlcurrents coming from lines L and L through coupling condenser 6, andboth the antenna frequency and the control frequency are then impressed,as will be seen from the drawings, upon the detector tube I by means ofthe broad band or untuned transformer 34. In Figure 2, other circuitelements which might have been shown to the left of tube I are omittedfor the sake of clarity, but they are identical in character andfunctioning to the similarly situated mixing box and receiver circuitdescribed and claimed in Patent No. 1,856,310. It will be clear that theinsertion of the tube 5 between the line L L and the antenna Asubstantially prevents any high frequency line control current fromreaching the antenna, and any radiation of the control frequencies fromthe antenna is thus substantially prevented. Another modification isillustrated in Figure 2a from which it will be observed that the highfrequency control currents generated in the control device C andtransmitted therefrom over the light or power lines L and L to themixing box apparatus generally indicated at M are impressed upon theplate circuit of the detector tube I instead of being impressed upon thegrid circuit of this tube as described in the patent aforesaid. If thehigh frequency control currents are of large amplitude, as is the casein the class of remote control systems herein considered, they will berectified between the plate and cathode electrodes of the vacuum tube I,the latter in the previous modification of the invention as described inconnection with Figure 2 it will be clear that by thus impressing thecontrol currents in the plate circuit of the tube while impressing theantenna signal currents in the grid circuit thereof, thecontrol-currents are prevented by the one-way repeater action of thetube from reaching the antenna and interference by these controlcurrents on neighborhood receivers is thus prevented. In Figure 2a, asin Figure 2, for the sake of clarity, certain circuit elements of themixing box and the receiver associated therewith have been omitted, butnevertheless the attachment to the circuit elements shown will be clearto those skilled in the art by referring to the aforesaid patent.

A third modification which may be employed to prevent radiation of thecontrol frequencies from the receiving antenna is shown in Figure 2b. Inthis arrangement, which for the sake of simplicity shows only thecircuits of the detector or mixing tube I, the control currents comingover the lighting lines (not shown in the figure) are fed to coil Nthrough the leads X and Y and fixed condenser K the latter being used toprevent short circuit of the low frequency (e. g. 60 cycle) linecurrent. The control frequencies are inductively transferred from coil Nto coil N. which is connected to the electrical center of coil 4 asshown which latter picks up incoming signal frequencies from the antennaA through its inductive relationship to coil 0. The condenser K isconnected as shown and given a value equal to the equivalent capacity ofthe grid condenser 2 and the capacity of the grid to cathode of tube Iin series; so that the impedance and phase angle of the upper circuit P2 P, N is substantially equal to the impedance and phase angle of thelower circuit P K and P N.

With this balanced arrangement it will be clear that the high frequencycontrol currents induced in coil N will divide equally between the upperand lower halves of coil 4. Half of the control current will flow upwardin the upper half of coil 4 and half the current will flow downwardthrough the lower half of coil 4 as indicated by arrows in the figure.These two portions of the control current therefore exactly neutralizeeach other in their effect upon the coil 0 which is so located as to beelectrically influenced equally by the two halves of coil 4. Thus, nocurrents of the control frequencies appear in the antenna andneighborhood interfence due to control frequency radiation from theantenna is avoided. While it is recognized that somewhat similar methodshave been used in other devices and for other purposes, the design heredisclosed for the specific purpose set forth is new and useful.

Cross-talk between circuits. (See Figure 3).- This type of interferencemay be experienced under the following typical conditions. Imagine twoadjacent apartments separated by a wall with houselightcircuits foreach, apartment located. in

the separating wall, and each apartment equipped with a remote controlsystem for radio reception comprising respectively the control units Cand C receivers and mixing boxes R and R antenna A and A and grounds Gand G Under certain circumstances it may be found thatthe high frequencycontrol currents flowing in the lighting circuit L, for example willaffect the operation of the receiver in apartment #2 or vice versa. Ihave termed interference of this kind crosstalk between circuits becauseit would appear at first sight that any such interference is the resultof induction between the two very closely adjacent line circuits L and LThe term is misleading, however, but its chief justification lies intheeasy picturization of the effect suggestion; for I have discovered thatthe lighting lines L and L exhibit practically no radiation of highfrequency energy whatever and furthermore that the effective couplingbetween them is negligibly small so that as a result any interference ofone control system on the other is not caused by any direct cross-talkor line to line effect. I have discovered that when this type ofinterference or apparent cross-talk is experienced, the reason for theeffect is that the two apparently independent lighting circuits are notin fact independent but are in some manner incidental to the wiring ofthe lighting system actually connected together as indicated generallyby the dotted lines L. The path of this concealed conection may be quitecircuitous and may pass through fuse blocks in the building, lineswitches, ground or accidental connections on the electric system, etc.but if such a path exists, the high frequency control currents generatedby a remote control unit such as C Figure3, and impressed by it upon thelines will follow around the lines and connecting path referred to andcause interference in another radio receiving system such as R It willnow be clear that the remedy to prevent this type of interference is ingeneral to segregate electrically each radio control system so that thehigh frequency control currents of each such system are prevented frompassing along the light lines beyond that portion of the house wiring tobe utilized in that particular system of remote control operation.

Figure 4 shows an arrangement used to accomplish the above result. Inthis figure there are shown, for the sake of clarity, two adjacent lightor power line circuits L and L connected through line switches S and Sand fuse blocks F and F to a common power supply line L which may runoutside of the building to a pole line transformer. Remote control unitsC are indicated as plugged into the lines L and L and radio receivers Rwith mixing boxes M are also shown as connected to the lighting lines.The

actual house wiring circuits will in general be much more complex thanhere indicated but the important fact is that in any system of two ormore such lighting or power circuits there is a point of commonconnection between them at the main power supply line such as indicatedat L and each such circuit is readily accessible at the point in thebuilding where its meter, switch, and fuse blocksare located. At suchpoints, therefore, I propose to insert isolating units so constructedand connected as to prevent the passage beyond them of the highfrequency control currents. Such units are indicated at I in Figure 4and their details of construction are shown in Figures 5 and 5a.

In Figure 5 the light lines coming from the portion of the lightingsystem in the building which is being used in the remote control radiooperation are indicated at L These are connected to the isolating unit Iand then pass on to the line switch of the system at 8 and 9. Theisolating unit comprises the-inductance coils 8a. and condensers 8b-8bconnected as shown with the coils in series with the two sides of theline and the condensers across the line. Such a combination of coils andcondensers when suitably designed in accordance with principles alreadyknown in the art will effectively prevent the passage of high frequencycurrents from the lines L to the points 3 and 9 and thus prevent theline to line cross-talk type of interference hereinabove referred to. Itwill be understood by those skilled in the art that other arrangementsand combinations of inductances and capacities may also be effectivelyemployed in this connection and located similarly in the system toaccomplish the result.

A uniquely similar arrangement to that of Figure 5 which functions inthe desired manner and which is more simple, is illustrated in Figure5a. It will be seen that herein the grounded side 9 of the lighting linehas no inductance coil in it, and that only one such coil Bet is hereused and that is placed in the ungrounded side 8 of the line.

While the arrangements just described are generally suitable forpreventing cross-talk, it has been found that in many cases the spiralinductance or choke coils'referred to may be dispensed with altogether.I have discovered that this is possible when the electric lightcompanies watt-hour meter separates the light line over which the remotecontrol operation is being conducted from other circuits for the reasonthat such standard meters possess sufficient inductance withinthemselves to serve as choke coils and effectively prevent the undesiredcross-talk phenomenon. In such cases it is usually satisfactory also todispense with the use of condensers. In other Words, when lightingcircuits are separately metered the choking effect of the metersthemselves to the high frequency control currents is in many casessuificient to prevent the passage of the latter from one metered circuitto another and cross talk is thus automatically prevented without theuse of additional apparatus.

Conjugate signal beats.In order to explain the nature of this type ofinterference one may consider, for example, the case in which remotecontrol operation is being conducted with respect to signals transmittedon frequencies within the present American broadcast band, viz. between550 kilocycles and 1500 kilocycles, and assume that the radio receiverportion of the entire remote control organization is pretuned to, say540 kilocycles, in accordance with the principles referred to in PatentNo. 1,856,310. Now any signal within the broadcast band may be heard onthe receiver by regulating the remote control frequency so that itdiffers from the desired incoming signal frequency by 540 kilocyclesthus creating the 540 kilocycle beat frequency to which the receiver isresponsive. Obviously, however, any frequency differing from the saidsignal frequency by 540 kilocycles, if superposed upon the desiredantenna signal frequency will produce'the same result, that is willproduce a beat frequency of 540 kilocycles with the signal andaccordingly cause reproduction of the latter by the receiver. Going astep further, it is apparent that any two high frequency currentssimultaneously impressed upon the mixing detector of the remote controlsystem and differing from each other by 540 kilocycles will result inenergy passing into the radio receiver, which as explained has beenpretuned to this frequency.

Thus it appears that many pairs of broadcasting stations may causeinterference with one another since the antenna pick-up organization ofthe remote control system is made substantially equally responsive toall broadcast frequencies and of these there are many conjugate pairs offrequencies differing by 540 kilocycles. Thus, a broadcastingtransmitter using a frequency of 800 kilocycles may produce a 540kilocycle beat frequency at the mixing detector with anotherbroadcasting station using a transmission frequency of 1340 kilocycles.Similarly, a I10 kilocycle broadcaster, for example, may also produce a540 kilocycle beat with a broadcaster using 1250 kilocycles; and otherstations transmitting simultaneously may produce 540 kilocycle beatsbetween themselves in the same way.

Obviously under these conditions many 540 kilocycle beat frequencies maybe superposed upon one another in the receiver, each variously modulatedin accordance with the speech or music characteristics of the varioustransmitting stations with the anticipated result that very seriousinterference may be produced in the form of unpleasant andunintelligible jumbling or intermixing of many programs from the outputof the receiver. Furthermore, the situation would seem to be stillfurther complicated by the presence in the system of another 540kilocycle beat which is that produced by the remote control when it 15adjusted to tune in various desired signals.

The present invention permits the mitigation of the conjugate beatfrequency interference described utilizing the circumstance, Federallyregulated, that broadcasting transmitters use frequencies of evenlynumbered kilocycles and are separated by ten kilocycles; it permits theelimination of this type of interference by using a beat frequency forremote control tuning which is higher than the frequencies used for thestipulated broadcasting; and it provides for the suppression of theinterference described by a. novel manner of using the mixing detectortube of the system.

For the mitigation of conjugate frequency interference I pretune thereceiver element of the remote control system to a frequency which,measured in kilocycles, is an odd multiple of 5, such for example as 545kilocycles. Now since broadcasting stations, in accordance with Federal.

regulations, use frequencies spaced ten kilocycles apart and havevalues, measured in kilocycles, which are even multiples of 5, it isclear that no pair of broadcast frequencies can combine to produce abeat frequency equal to that to which the receiver has been pretuned.The nearest beat frequency which can thus be produced will be 5kilocycles different from the frequency to which the receiver has beentuned, and depending upon the sharpness or selectivity of the receiveritself therefore, conjugate signal beats will be more or less reduced intheir interference effects upon the receiver.

For the elimination of conjugate broadcast frequency beats it isproposed to pretune the receiver to a frequency above the highest signalfrequency to be received. For example, in broadcast reception thereceiver may be tuned to say 1520 kilocycles. Since the broadcastfrequency band referred to runs from 550 to 1500 kilocycles it is clearthat no conjugate frequencies exist within this band whose differencecan be as large as 1520, kilocycles and in this way, therefore, thepossibility of interference of the kind considered is eliminated.

For the suppression of conjugate broadcast frequency interference Iemploy the novel and useful expedient of polarizing the mixing detectorof the system with a strong high frequency voltage in a manner such thatthe detector output varies in direct proportion. to its input. 1 This isaccomplished by causing the detector to oscillate by the use of methodsand principles well lmown in the art, orby impressing upon it a stronghigh frequency oscillation from another source such as from the remotecontrol unit over the connecting light or power circuit. Certain circuitarrangements are also made at the detector, according to knownprinciples which to-., gether with the polarizing valtage referred tocause the operation of the detector to take place on a linear portion ofits effective rectification characteristic.

The action and principle involved will be clear by reference to Figure 6in which the line 0-? represents the effective rectificationvcharacteristic of the detector following a non-linear law near 0 forsmall impressed voltages and a practically linear law for largeimpressed voltages. The abscissas of this rectifier curve representimpressed voltages on the detector while the ordinates to the curverepresent corresponding outpu currents from the detector. 1

Assume first, for example, that only two signal frequencies areimpressed upon the detector; that they are impressed simultaneously;that, for the sake of simplicity, they are unmodulated, and that one hasa frequency of say 800 kilocycles and the other 1340 kilocycles. Thevoltage resultant of these will be as shown at a with a beat frequencyenvelope of 540 kilocycles and as a result of rectification the detectoroutput current will be as shown at b containing a 540 kilocyclecomponent as indicated by the lower dotted line, and this 540 kilocyclecomponent wiil thus be amplified by the receiver connected to the outputof the detector, assuming, of course, that the receiver has beenpretuned to 540 kilocycles. This is the condition that would beexperienced when the detector is used in the ordinary conventionalmanner with non-linear response, and gives rise to the conjugate signaibeat interference hereinabove described since any two signal frequenciesdiffering by 540 kilocycles simultaneously impressed upon the detectorwill produce the 540 kilocycle variation in detector output current.

Now, however, if there is also impressed upon the detector theunmodulated high frequency polarizing voltage 0 of Figure 6 the actionis entirely changed. The total voltage impressed upon the detector isnow the sum of a and c, which after rectification results in the platecurrent 0!. .It will be seen that in this plate current there are two540 kilocycle components which are oppositely phased and as a resultthereof no 540 kilocycle current reaches the amplifier. The effect ofthe polarizing oscillation therefore, and the resulting linear detectorresponse causes complete suppression of the 540 kilocycle beat betweenthe two representative signals of 800 kilocycles and 1340 kilocyclessimultaneously impressed detector.

I Cross modulation-This is an interference effeet which may manifestitself on a remotely controlled receiver of the class herein consideredduring the process of tuning in various stations when reception is beingcarried on in the vicinity of a high power broadcasting station. It isusually noticed only when the receiver is located within a mile or so ofsuch a transmitter. It comprises a phenomenon not alone peculiar toremote control operation of a receiver but is also often encountered inthe conventional operation of ordinary receivers. When it occurs theoperator of the receiver will notice that while he may be able to tuneout the strong local station by a relatively small adjustment of thetuning of the receiver, nevertheless when he successively tunes in othersignals the local signals will be heard on the superposed upon the otherstation to which he tunes the receiver. In fact the local station may beheard atmany different settings of the receiver tuning mechanism thoughonly at such settings as may correctly tune in a station other than thelocal. This type of interference by a local station with another stationthough the two be using widely different transmission frequencies hasbeen well known in the art for some time and it may, as stated, readilyoccur in remote control systems of the class herein considered in thefollowing way:-

' In such systems, the pick-up organization at the mixing detectorcomprising coils of the general class of 3 and 4 of Figure 1 and morefully described in Patent No. 1,856,310 constitutes an untuned orbroad-band tuned receiving circuit connected to the antenna A anddetector tube I; and all antenna signals or broadcast programs withinthe band of frequencies which it may be desired to receive are herebypassed to the detector tube By the process of detection these signalsare broken up into currents of various component parts, there beingproduced, among other currents in the detector circuit, audio frequencycurrents of the various audible frequencies that were present in themodulation characteristics of the original incoming signal wave. Thiscircumstance exists for all signals received upon the antenna. Now bythe process of remote control tuning herein considered the carrierfrequency of an antenna signal is changed by intermixing with the lightline control frequency to a new (beat) frequency suitable foramplification by the receiving set and, as explained in the patentpreviously referred to, this new (beat) frequency first appears in theplate circuit of the mixing box detector tube I, Figure 1. It will beclear, therefore, that the plate circuit of this tube contains currentsof a great many different frequencies. Those of most importance,however, are the beat frequency just referred to as produced in thereception of some desired transmitting station, and any extremely strongaudio frequency currents that may be produced by a powerful localtransmitting station.

If the amplitude of the last mentioned audio currents is so great as tobe ten percent or so of the amplitude of the beat frequency carriercurrent produced in the reception of another station then it will bereadily understood that these audio currents will be suniciently strongto modulate the beat frequency carrier current through the superpositionof the two and the local station will therefore be audibly overlayed onthe other station which it is desired to receive. This constitutes thecross-modulation type of interference, the suppression of which is oneof the objects of this invention.

To suppress this cross-modulation type of interference I make use of thelinear detection action and polarizing oscillation hereinbeforedescribed with reference to the suppression of conjugate signal beats,and through the use of the detector in this way cross-modulation isprevented in a manner entirely similar to the suppression of conjugatesignal beats. The action and principle involved in this case will beclear by reference to Figure 7. In this figure the desired carrierfrequency current, shown umnodulated, for the sake of clarity, isindicated at a. The polarizing oscillation, here assumed for convenienceof drawing as differing from the desired carrier by 540 kilocycles isshown at b. The superposition of these and rectification of theirresultant produces the detector output current a with high frequencyenvelope of 540 kilocycles. Under the assumption that the receiverhasbeen pretuned to 540 kilocycles the desired signal carrier thuschanged to 540 kilocycles will now be amplified by the receiver.

Now upon additionally impressing the modulated signal (1 which mightnormally be expected to produce cross modulation the output current fromthe detector obviously takes the form e, at least as far as the 540kilocycle envelope is con-.- cerned, and it is at once evident that thelatter is not modulated by the audio component of the interferencesignal.

As in the suppression of conjugate signal interference, it will be clearthat here too the requirement for suppression of interfering signals isthat the polarizing oscillation be of large amplitude as compared withthe interference and that the detector response be linear rather thancurved in the region of operation.

It will also be understood that the frequency of the polarizingoscillation may have any value so long as it is above audibility anddoes not produce audible frequency beats withany of the otherfrequencies involved in the operation of;

the system. I

Image signals The general nature of this type of interference may bemade clear by the following example. Suppose that the receiver of theremote control system is pretuned to a relatively low frequency such as,say 175 kilocycles, instead of to the higher beat frequencies heretoforeconsidered, and suppose it is'desired to receive an 800 k. c.broadcasting signal according to the principle described by superposingupon this 800 k. 0. signal frequency another frequency differing by 1'75k. 0. so as to produce a beat frequency of the latter value suitable forthe pretuning setting of the receiver. The superposed frequency for thispurpose may thus be 975 k. c., that is 175 k. c. above the desiredsignal frequency. It will be clear, however, that this superposedfrequency of 9'75 k. 0. can also produce a 175 k. 0. beat with anotherbroadcast signal of 1150 k. 0. so that the latter as well as the desired800 k. 0. signal will both be amplified and reproduced by the receiverand thus cause interference. This is image interference, and the twobroadcast signal frequencies of p 800 k. c. and 1150 k. c. are said tobe image fre-, quencies. It is to be noted that they differ from oneanother by twice the value of the beat frequency used for tuning.

In the example just cited it is obvious that the reason for theexistence of the image interference as described for broadcast bandreception, 1. e. for reception of signals between 550 k. c. and 1500 k.0., is that the beat frequency employed is so low, that is 175 k. c.;and it follows equally clearly that such broadcast image interferencecan be prevented by selecting a higher beat frequency for the tuningprocess such as frequencies in the neighborhood of 540 k. c. or elseabove 1500 k. c. as have hereinbefore been discussed and fully explainedin Patent No. 1,856,310,

When the beat frequency used is as high as say 540 k. c. it isimpossible to experience broadcast images and the use of beatfrequencies of this order of magnitude and for this reason is thereforean important, novel and useful feature of the present invention. Thus,if the beat frequency used for the tuning process is say 540 k. c. (i.e. the receiver is pretuned to 540 k. c.) the control beating or tuningfrequencies used for broadcast reception will run from 1090 k. c. for550 k. c. reception up to 2040 k. c. for 1500 k. 0. reception and signalfrequencies which would produce image interference accordingly liebetween 1630 k. c. and 2580 k. c., a frequency band entirely outside ofthe broadcast range. It will be clear that in order to avoid broadcastimage interference of the kind described the beat frequency used in thetuning process must be above 475 k. c. for at this frequency the tuningcontrol frequency required for 550 k. c. reception would be 1025 k. c.which would bring in an interfering image at 1500 k. c., the lowestbroadcasting frequency used.

While image interference within the 550 k. e. to 1500 k. c. broadcastband is impossible in the present system due to the use of relativelyhigh beat frequency in the manner and for the reasons described, thereis nevertheless the possibility of image interference from various shortwave transmitting stations such as those used for picture transmission,amateur radio communication, etc. Thus, in the example above statedwhere a beat frequency of 540 k. c. is used, it was shown that imageinterference would be caused by transmitting stations using frequencieswithin the band 1630 k. c. to 2580 k. c. Similarly if the beat frequencyemployed is at the other end of the breadcast band, such for example atsay 1520 k. c., then obviously short wave image interference is possiblefrom transmitters using frequencies between 3590 k. c. and 4540 k. c.

In order to prevent short wave image interference of this kind I use, inone modification of my invention a low-pass filter in the antennacircuit preceding the mixing detector as indicated in Fig. 8. Herein Ais the receiving antenna, G the ground, and the organization at M themixing tube and input circuits as hereinbefore described. The low-passfilter is indicated generally at F It is designed according toprinciples well known in the art and in a manner such that frequenciesbelow 1500 k. 0. pass readily from the antenna to the mixing detectorwhile frequencies above 1500 k. c. are substantially blocked out andprevented from reaching the detector. It is to be understood, of course,that the design described applies specifically to the case where thesystem is intended for the reception of the usual broadcast signalsusing frequencies from 1500 k. c. to 550 k. c. For other conditions ofuse the same filtering principle may be used for similar purposes andthe design of the filter will be carried out according to knownprinciples such that desired frequencies will be passed to the detectorwhile interfering signals will be suppressed.

An alternative arrangement to that of Fig. 8

which also provides for the suppression of interference by short wavesby preventing such short wave frequencies from reaching the mixingdetector is shown in Fig. 9, where it will be seen that an additionalvacuum tube V is inserted between the antenna and the low-pass filterwhich latter may now consist, as shown, of the choke coil F andcondensers C and C This arrangement has certain advantages over thearrangement of Fig. 8 in that the filter is hereby removed from theantenna circuit whose electrical characteristics may be such, as will beunderstood by those skilled in the art, as to reduce the effectivenessof the filter if placed directly in the antenna circuit. Furthermore,the arrangement of Fig. 9 with the filter and tube V interposed betweenthe antenna and the mixing detector V assists in preventing radiationfrom the antenna of the high frequency control frequencies coming overthe light lines and delivered thence to the circuits of the detector.

H armom'c interference I have pointed out in my Patent No. 1,856,310that in the operation of the remote control system as described, thecircumstance that the ratio of maximum to minimum control tuningfrequencies for broadcast reception is less than 2 to 1 prevents thepossibility of interference which might otherwise result from a harmonicof the remote control oscillator producing a beat frequency suitable foramplification by the receiver of the system by combination of such aharmonic with another broadcast frequency other than the one which itmay be desired to receive. It will be understood, however, that if theremote control oscillator generates harmonics, interference may beexperienced thru the combination of such harmonies with short wavetransmitters of the class referred to hereinabove with respect to shortwave image interference, provided such harmonics produce a beatfrequency or frequencies with such short wave signals equal to thefrequency to which the receiver has been pretuned for remote controloperation.

When such harmonic interference is experienced I prevent it bysuppressing harmonic frequencies of the remote control oscillator byarranging that its output energy be substantially sinusoidal as tooscillation wave form. This may readily be accomplished by methods wellknown in the art. Alternatively for the same purpose I suppress theinterfering short wave signals coming in on the antenna, and for thispurpose use the same arrangements as shown in Fig. 8 and Fig. 9hereinbefore described with respect to suppression of short wave imageinterference. It is to be understood therefore that the arrangements ofFig. 8 and Fig. 9 are employed to prevent both short wave image signalsand short wave harmonic interference. This is possible because the shortwave frequencies capable of producing harmonic interference lie in arange above approximately the value of any possible image frequencysignals. Thus, for a 540 k. 0. beat frequency at the receiver it hasbeen shown that possible image producing frequencies for broadcast re-'ception lie above 1630 k. 0., whereas for this same receiver beatfrequency the possible harmonic interference signals lie above 1640 k.c. because the remote control frequency required for the reception ofthe longest wave broadcasted which uses 550 k. c. is obviously 1090 k.c. of which the second harmonic is 2180 k. c. and the lowest shortproduce a 540 k. 0. beat is obviously 1640 k. c.

Static and background interfercnce.'I'his class of interference iscommonly experienced in the operation of all radio receivers. In a remotely controlled receiving system, however, of the kind hereinconsidered, a somewhat different situation is presented in respect tothis kind of interference, and in connection with such systems I use asimple expedient to minimize or reduce this interference.

' This expedient embodies a detail in the method of operating the remotecontrol system. If static, damped wave spark signals, or otherbackground interference or noise is present, I turn the volume controldevice of the receiving set down until such background noises are notannoying. This control is. then left at that setting for the receptionof all stations. This of course makes it impossible to receive desiredstation signals by remote control as loudly as if the volume control onthe receiver itself were turned up to maximum. However, under heavystatic or bad background noise conditions it is not possible to use thevolume control on the receiver at its maximum position even in theconventional direct operation of the receiver, and it is plain thereforethat as regards such interference the remote control system operated asdescribed in reference to the permanent adjustment of the receivervolume control device is on a par with the ordinary directly operatedreceiver. This detail of adjusting the receiver volume control asdescribed is simple, but it is an interference preventing expedient inremote control operation which may not be obvious.

While the method just described for minimizing static and backgroundnoise is useful and simple, it does not provide the flexibility affordedby the direct continuous operation of the actual volume control on thereceiver as normally practised in the conventional operation of thereceiver to alter its sensitivity and thus limit the amount ofbackground noise or static. The reason for this is that withthe methoddescribed it is clearly impossible by means of the remote controloscillations, to increase or decrease the sensitivity of the receiveritself. An improvement therefore upon the method described would be anarrangement permitting actual control of the sensitivity of the receiveritself.

One modification of such an arrangement which I have employed is shownin Fig. 10, which shows the elements at the receiver essential to theaccomplishment of the object stated. The remote control unit (not shownin the figure but constructed and used generally according to theprinciples described'in my Patent No. 1,856,310) generates a suitablehigh frequency current to be used for controlling the sensitivity orgain of the receiver. This control current is delivered to the receiverorganization over the leads :2 and y and thence to the circuit LC whichis designed to be responsive to the said control current. The lattercircuit is connected as shown to the auxiliary rectifier tube T. Thehigh frequency control currents are thus rectified at T and according towell known principles produce a continuous D. C. potential across theresistance R. A portion of the circuits of the radio frequency amplifierof the receiver is shown connected to this resistance, and it will beclear from the drawings that thru the connections of the amplifier tothe resistance R the D. C. voltage drop thru the latter will affect thegrid bias voltage on the tubes of the amplifier and hence theamplification of the latter. The larger the amplitude of the highfrequency control current (this being controllable at the remote controlpoint according to the principles explained in my Patent No; 1,856,310)the greater will be the D. C. voltage across the resistance R and hencethe greater the negative bias on the tubes of the amplifier in thereceiver; and the smaller the amplitude of the control current the lesswill be the amplifier tube bias. It will thus be clear that by suitablylocating the tap P permanently on the resistance R a condition mayreadily be established such that when the control current referred to isof zero amplitude the bias voltage on the amplifier is correct formaximum receiver amplification, while with large control currentamplitude this bias voltage assumes a sufficiently large negative valueto prevent amplification by the tubes of the receiver. The actualreceiver sensitivity is thus altered by changing the amplitude of thecontrol oscillation at the control point which in turn changes the gridbias of the amplifier. Immunity from background noise and static, aswell as volume control of the receiver is thus achieved by an actualchange in receiver performance entirely similar to that by normal directoperation of the receiver by means of its own controls.

A variation of the arrangement just described is shown in Fig. 11, butWorks in the reverse way. That is, in the arrangement of Fig. 11 thestrength of signal delivered by the receiver, or otherwise stated, itssensitivity decreases with decreases made in the amplitude of thecontrol oscillation at the remote control point. This has certainadvantages over the method illustrated by Fig. in that it permits theuse, if desired, of the tuning currents generated and operativeaccording to the principles of my Patent No. 1,856,310 for remotecontrol of receiver sensitivity as well. As these tuning currents arere-' duced at the remote control point the signal strength at thereceiver is decreased for two reasons. First the volume is reducedbecause the amplitude of the beat frequency at the receiver resultingfrom the mixing of the control tuning current and the antenna signalcurrent is reduced, and second, the grid bias on the receiver amplifiertubes becomes more negative due to the increase in the plate current ofthe leaky grid volume control rectifier tube D thru resistance R, Fig.11, which reduces the amplification of the receiver.

H I shall now describe in detail a modification of the present inventioncomprising a complete remotely controlled receiver system in which allof the several features for preventing the various kinds of interferencehereinbefore described are included. Reference is made to Fig. 12. AtRFA is shown a portion of the conventional circuits of the radiofrequency amplifier portion of a radio receiver. These circuits areconnected as shown to an organization of auxiliary circuits whichinclude among other elements the mixing detector tube ill and the volumecontrol tube ll, each with their respective grid condensers I 2 and i2and grid leaks l3 and it. The batteries B 13 B are merely shown as suchto indicate the points in the circuits where plate voltage is suppliedto the several tubes, and it will be undering to principles and methodswell known in the art. The remote control unit is indicated at C and inaccordance with the principles of my Patent No. 1,856,310 is arranged togenerate simultaneously a certain fixed frequency of invariableamplitude and also other frequencies used for tuning, variable at willby the operator for tuning in various stations at the receiver, andadjustable in amplitude to regulate the volume or strength of signalsreproduced by, the receiver. Both the fixed frequency and the tuningfrequencies just referred to are sent over the lighting lines L and L tothe receiver organization where they are injected into the latter thrucoils l4 and I5 acting inductively respectively upon the associatedcoils l4 and IS. The latter are in the central leg of the bridge circuitcomprising tube In, center tapped coil I5 and condenser I1 arranged ashereinbefore described to prevent radiation from the antenna of anycontrol current frequencies. The tuning frequencies are introduced intothe receiver circuits thru the coil combination l4l4, while the fixedfrequency from the control point is introduced into the receivercircuits thru the coil combination l5l 5, the latter being tuned to thesaid fixed frequency by means of condenser IS. The antenna signalcurrents are led to coil l6 from the antenna A thru the low-pass filterconsisting of coils l9-l9 and condensers 2G2l-22 as hereinabovedescribed with reference to and for the purpose of suppressing shortwave image and harmonic interference. Since the circuit l5--l8 is tunedas stated to the fixed frequency delivered from the control unit aconsiderable high frequency voltage of this fixed frequency is developedacross this circuit, and this steady high frequency voltage continuouslyapplied to the detector tube H] as will be clear from the drawingsserves to polarize the detector tube I and suppress both crossmodulationinterference and interference from conjugate signal frequencies in theantenna in accordance with the principles hereinabove explained withreference to the elimination of these types of interference. In seriesin the tuned circuit |5|8 is the thermal switch 23 operative accordingto the principles explained in my Patent No. 1,856,310 which as shown inthe drawings Fig. 12 closes the circuit to supply power to the entirereceiver organization. Radio frequency choke coils 24 are inserted atthe points in the circuits shown to prevent the passage of highfrequency currents into portions of the system from. which it isobviously necessary to exclude them. The input voltage to the volumecontrol tube II is the voltage developed across the coil M by the tuningcurrents from the remote control point, this voltage being impressedupon the tube ll thru the lead wire 25. When the ampli tude of thetuning currents fed into the line at the remote control point is reducedthe beat frequency tuning current produced by detector tube l 0 fed tothe receiver amplifier thru condenser 26 decreases and hence reduces thevolume of whatever signal has been tuned from the control point. At thesame time this decrease in tuning frequency amplitude reduces the highfrequency input to the volume control tube ll, increases the platecurrent of this tube thru the resistance 21, accordingly increases thegrid bias on the amplifier portion of the receiver, and hence reducesthe receiver sensitivity so that all signals including those produced bystatic or other background noise are reduced, and vice versa when thetuning currents from the control point are there increased in amplitude,the signals from the receiver are increased.

Without further description it is thought that the features andadvantages of the invention will be readily apparent to those skilled inthe art, and it will of course be understood that changes in the form,proportion and minor details of construction may be resorted to, withoutdeparting from the spirit of the invention and scope of the appendedclaims.

I claim:--

1. In a remotely controlled radio receiving system adapted to becontrolled over an electric power supply line, the combination of areceiver having an antenna input circuit, and signal reproducingapparatus, control means for controlling said receiver, means forcoupling said control means to the power supply line at a point remotefrom said receiving apparatus, said control means including means forgenerating high frequency currents of various frequencies for renderingsaid receiver responsive to signal energy of different frequencies andmeans for generating a high frequency control current of fixedfrequency, both of which currents are impressed on the power supplyline, coupling means for connecting the signal input circuit of saidreceiver to an electric power supply line and means connected to theinput circuit of said radio receiver for preventing radiation of any ofsaid control current frequencies from the antenna of said receiver.

2. In a remotely controlled radio receiving system adapted to becontrolled over an electric power supply line the combination of areceiver having an antenna input circuit, and signal reproducingapparatus, control means for controlling said receiver, means forcoupling said control means to the power supply line at a point remotefrom said receiving apparatus, said control means including means forgenerating high frequency currents of various frequencies for renderingsaid receiver responsive to sign-a1 energy of different frequencies andmeans for generating a high frequency control current of fixedfrequency, both of which currents are impressed on the power supplyline, coupling means for connecting the signal input circuit of saidreceiver to an electric power supply line; and means connected to theinput circuit of said receiver, including a tuned circuit tuned to thefixed frequency delivered from the control means, for suppressingcrossmodulation interference between signal frequencies and frequenciesgenerated by said control means.

3. In a remotely controlled radio receiving system adapted to becontrolled over an electric power supply line, the combination of areceiver having an antenna input circuit, a detector tube, and signalreproducing apparatus, control means for controlling said receiver,means for coupling said control means to the power supply line at apoint remote from said receiving apparatus, said control means includingmeans for generating high frequency currents of various frequencies forrendering said receiver responsive to signal energy of differentfrequencies and means for generating a high frequency control current offixed frequency, both of which currents are impressed on the powersupply line, coupling means for connecting the signal input circuit ofsaid receiver to an electric power supply line; and means connectedtothe input circuit of said receiver including a tuned circuit tuned tothe fixed frequency delivered from the control means to supply a steadyhigh frequency voltage to said detector tube of said receiver forpolarizing said detector and suppressing cross-modulation interferenceand interference from conjugate signal frequencies in the antenna.

4. In a remotely controlled radio receiving system adapted to becontrolled over an electric power supply line the combination of areceiver having an antenna input circuit, a detector tube, and signalreproducing apparatus, control means for controlling said receiver,means for coupling said control means to the power supply line at apoint remote from said receiving apparatus, said control means includingmeans for generating high frequency currents of various frequen-- ciesfor rendering said receiver responsive to signal energy of differentfrequencies and means for generating a high frequency control current offixed frequency, both of which currents are impressed on the powersupply line, coupling means for connecting the signal input circuit ofsaid receiver to an electric power supply line; means including a tunedcircuit tuned to the fixed frequency delivered from the control means,in circuit with said radio apparatus to suppress crossmodulationinterference and interference from conjugate signal frequencies in theinput of said receiver, and a thermal switch connected in series withsaid tuned circuit for controlling the power from the power lines tosaid receiver.

5. In a remotely controlled radio receiving system adapted to becontrolled over an electric power supply line the combination of areceiver having an antenna input circuit, a detector tube, a volumecontrol tube, and signal reproducing apparatus, control means forcontrolling said receiver, means for coupling said control means to thepower supply line at a point remote from said receiving apparatus, saidcontrol means including means for generating high frequency currents ofvarious frequencies for rendering said receiver responsive to signalenergy of different frequencies and means for generating a highfrequency control current of fixed frequency, both of which currents areimpressed on the power supply line, coupling means for connecting thesignal input circuit of said receiver to an electric power supply line;and means connected to said coupling means for selecting and impressinghigh frequency potentials generated at said control means on the inputcircuit of said volume control tube for controlling the operationthereof.

6. A remotely controlled radio receiving system comprising incombination, a radio receiver having an antenna and being connected toelectric light or power lines, means for generating highfrequencycurrents of various frequencies at a point remote from the saidreceiver, means for coupling said generating means with the light orpower lines, means at said remote point for varying the strength of saidhigh-frequency currents, means in circuit with said receiver circuitsand with said power or light lines comprising a rectifier, means forconnecting said rectifier to said radio receiver for controlling theamplification thereof, means for impressing certain of the remotelygenerated high-frequency currents on the power lines, means forimpressing high-frequency signal voltages from the antenna upon theinput of the circuits of both the aforesaid rectifier and thermionictubes, filter means having predetermined electrical characteristicsconnected in circuit with the antenna and adapted substantially toprevent the flow of undesired ones of said high frequency currents intothe antenna, and means connected with the receiver apparatus andresponsive to high-frequency currents generated at the said remote pointadapted to close or open the light or power line supply circuit to thesaid receiver apparatus.

ALBERT S. BLATTERMAN.

